<!DOCTYPE HTML>
<html>
	<head>
		<title>please enter your title</title>
		<meta charset="utf-8">
		<meta name="Author" content="潭州学院-阿飞老师">
		<style type='text/css'>
			*{ margin:0; padding:0;}
			
			#box{
				width:100px;
				height:100px;
				background:red;
				transition:background 2s;
			}
		</style>
	</head>
	<body>
		
		<div id="box">

		</div>

		<script type="text/javascript">
			
			box.onclick = function(){
				this.style.cssText = 'width:200px;height:200px;background:green;'
			}


		</script>
	</body>
</html>